The evaporation process is a common and primary process in industrial processes such as chemical industry, light industry, food manufacturing, pharmacy, and effluent treatment etc. The evaporation process consumes a great amount of steam, and is a high energy-consuming process. Since the evaporation process is far and wide applied in the process industry, the improvement of the energy utilization rate in the evaporation process plays a significant role in saving the energy, increasing the efficiency, and enhancing industrial competitiveness in the process industries such as petrochemicals and metallurgy etc.
At present, the technique for concentrating the solution by the evaporation method mainly includes multiple-effect evaporation technique and the mechanical vapor recompression technique. In the multiple-effect evaporation technique, the secondary steam produced by the earlier stage of evaporator is used as the heat source to heat the later stage of evaporator, and a plurality of evaporators are connected in series for operation, thus greatly reducing the steam use level. In the mechanical vapor recompression technique, the secondary steam produced by the evaporator is recompressed to improve the thermodynamic quality thereof, and reenters into the evaporator as heating steam to supplement or even completely replace the primary steam.
The multiple-effect evaporation technique can save a part of the primary steam, but the continuous steam supply is required for the first effect, and the secondary steam generated by the final effect is generally directly condensed and not utilized. Moreover, the more effects, the larger the equipment is, which increases the investment in the equipment. The mechanical steam recompression technique overcomes the waste caused by directly condensing and discharging the residual secondary steam of the final effect in the multiple-effect evaporation technique. The operating cost mainly includes the power consumption of steam compressor. However, the anti-rust and anti-corrosion protection of the key equipment, i.e. the steam compressor, and the safety and reliability under long-term operating conditions are tough problems to be solved.